1. Field of the Invention
The present invention relates to a low temperature yoke type tunnel valve sensor and, more particularly, to such a sensor wherein first and second copper structures conduct heat to at least one of two yoke layers wherein the yoke layers conduct a tunneling current (IT) to the tunnel valve sensor and transmit flux from an air bearing surface (ABS) to the sensor.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm urges the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a tunnel valve sensor for sensing the magnetic signal fields from the rotating magnetic disk. The sensor includes a nonmagnetic electrically nonconductive tunneling or barrier layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90xc2x0 to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the rotating disk. The tunnel valve sensor is located between ferromagnetic first and second shield layers. First and second leads, which may be the first and second shield layers, are connected to the tunnel valve sensor for conducting a tunneling current therethrough. The tunneling current is conducted perpendicular to the major film planes (CPP) of the sensor as contrasted to a spin valve sensor where a sense current is conducted parallel to the major film planes (CIP) of the spin valve sensor. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic signal fields from the rotating magnetic disk. The quiescent position of the magnetic moment of the free layer, which is parallel to the ABS, is when the tunneling current is conducted through the sensor without magnetic field signals from the rotating magnetic disk.
When the magnetic moments of the pinned and free layers are parallel with respect to one another the resistance of the tunnel valve sensor to the tunneling current (IT) is at a minimum and when their magnetic moments are antiparallel the resistance of the tunnel valve sensor to the tunneling current (IT) is at a maximum. Changes in resistance of the tunnel valve sensor is a function of cos xcex8, where xcex8 is the angle between the magnetic moments of the pinned and free layers. When the tunneling current (IT) is conducted through the tunnel valve sensor, resistance changes, due to field signals from the rotating magnetic disk, cause potential changes that are detected and processed as playback signals. The sensitivity of the tunnel valve sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in resistance of the tunnel valve sensor from minimum resistance (magnetic moments of free and pinned layers parallel) to maximum resistance (magnetic moments of the free and pinned layers antiparallel) and R is the resistance of the tunnel valve sensor at minimum resistance. The dr/R of a tunnel valve sensor can be on the order of 40% as compared to 10% for a spin valve sensor.
The first and second shield layers may engage the bottom and the top respectively of the tunnel valve sensor so that the first and second shield layers serve as leads for conducting the tunneling current (IT) through the tunnel valve sensor perpendicular to the major planes of the layers of the tunnel valve sensor. The tunnel valve sensor has first and second side surfaces which intersect the ABS. First and second hard bias layers abut the first and second side surfaces respectively for longitudinally biasing the free layer. This longitudinal biasing maintains the free layer in a single magnetic domain state and helps to maintain the magnetic moment of the free layer parallel to the ABS when the read head is in the quiescent condition.
Magnetic head assemblies, wherein each magnetic head assembly includes a read head and a write head combination, are constructed in rows and columns on a wafer. After completion at the wafer level, the wafer is diced into rows of magnetic head assemblies and each row is lapped by a grinding process to lap the row to a predetermined air bearing surface (ABS). In a typical tunnel valve read head all of the layers are exposed at the ABS, namely first edges of each of the first shield layer, the seed layer, the free layer, the barrier layer, the pinned layer, the pinning layer and the second shield layer. Opposite edges of these layers are recessed in the head. The barrier layer is a very thin layer, on the order of 20 xc3x85, which places the free and pinned layers very close to one another at the ABS. When a row of magnetic head assemblies is lapped there is a high risk of magnetic material from the free and pinned layers smearing across the barrier layer at the ABS to cause a short therebetween. Accordingly, there is a strong-felt need to construct magnetic head assemblies with tunnel valve heads without the risk of shorting between the free and pinned layers at the ABS due to lapping.
The present invention provides a read head which includes a tunnel valve sensor and first and second yoke layers wherein the tunnel valve sensor is recessed from the ABS and the first and second yoke layers are magnetically connected to the tunnel valve sensor and extend to the ABS for conducting signal fields from a rotating magnetic disk to the tunnel valve sensor. Because of the recessed location of the tunnel valve sensor, lapping of the head will not smear conductive material across the barrier layer of the tunnel valve sensor so as to short a tunneling current (IT) across the barrier layer. In a preferred embodiment, a first yoke layer below the tunnel valve sensor is wide at the ABS and maintains its width as it extends into the head from the ABS. The first yoke layer provides a heat sink for the tunnel valve sensor. In contrast, the second yoke layer is very narrow at the ABS so as to establish and define a track width of the read head and increases in width from the ABS to a magnetic coupling to the tunnel valve sensor. With this arrangement a very narrow track width can be obtained while the width of the tunnel valve sensor is large so as to reduce resistance of the tunnel valve sensor to the tunneling current (IT). From the tunnel valve sensor the second yoke layer maintains a larger width than the track width and provides another heat sink for the tunnel valve sensor. The distance between the first and second yoke layers at the ABS defines the read gap of the read head. This read gap is significantly less than when the tunnel valve sensor is located at the ABS and the read gap is defined by the distance between first and second shield layers. The narrow read gap enables more magnetic bits to be placed per linear inch along the track of the rotating magnetic disk. The narrow track width enables more tracks to be placed per inch along a radius of the rotating magnetic disk. A product of these two values, bits per inch (BPI) and tracks per inch (TPI), is the areal density of the read head. The first and second yokes enable a very high areal density which significantly increases the storage capacity of the magnetic disk drive.
The tunneling current (IT) is conducted between top and bottom surfaces of the tunnel valve sensor. The invention provides first and second copper (Cu) structures wherein the first copper structure interfaces the bottom surface of the tunnel valve sensor and the second copper structure interfaces the top surface of the tunnel valve sensor. Both of these copper structures are employed for the purpose of conducting heat from the tunnel valve sensor during its operation. There are two preferred embodiments of the present invention. In both embodiments the second copper structure conducts heat from the tunnel valve sensor to the second yoke layer. In the first embodiment, the first copper structure conducts heat from the tunnel valve sensor to the first yoke layer and in the second embodiment the first copper structure conducts heats from the tunnel valve sensor to a substrate.
Still further in the first embodiment the top surface of the tunnel valve sensor may have a middle portion located between front and back top surface portions. The second yoke layer has first and second yoke layer portions wherein the first yoke layer portion has a front surface that forms a portion of the ABS. The first yoke layer portion of the second yoke layer interfaces the front top surface portion of the tunnel valve sensor and the second yoke layer portion of the second yoke layer interfaces the back top surface portion of the tunnel valve sensor. The second copper structure interfaces the middle top surface portion of the tunnel valve sensor and each of the first and second yoke layer portions of the second yoke layer. With this arrangement heat from the tunnel valve sensor is quickly dissipated into the second copper structure, thence into the first and second yoke layer portions of the second yoke layer which function as heat sinks. Still further, in the first embodiment the first copper structure is located between and interfaces each of the bottom surface of the tunnel valve sensor and a top surface of the first yoke layer so that heat is quickly dissipated into the first copper structure, thence into the first yoke layer which functions as a heat sink. In the first embodiment a tunneling current (IT) source is connected across the second yoke layer portion of the second yoke layer and the first yoke layer so that the tunneling current is conducted between the top and bottom surfaces of the tunnel valve sensor.
In the second embodiment of the invention the first yoke layer has first and second yoke layer portions instead of the second yoke layer having first and second yoke layer portions. The second yoke layer is not divided into portions and extends from the ABS into the head across the top surface of the tunnel valve sensor. Between the top surface of the tunnel valve sensor and the second yoke layer is the second copper structure which absorbs heat from the top of the tunnel valve sensor and conducts it to the second yoke layer which functions as a heat sink. The tunnel valve sensor is located between the first and second yoke layer portions of the first yoke layer with the first yoke layer portion being located at the ABS and having a width that defines the track width (TW) of the read head. The distance between the first yoke layer portion of the first yoke and the second yoke layer defines the read gap of the read head and is significantly less than when the tunnel valve sensor is located at the ABS. Accordingly, the second embodiment can have high areal density similar to the first embodiment. In the second embodiment the first copper structure is located between and interfaces each of the bottom surface of the tunnel valve sensor and a top surface of a substrate which acts as a heat sink. Accordingly, heat from the bottom of the tunnel valve sensor is dissipated into the first copper structure, thence into the substrate. In the second embodiment the tunneling current (IT) source is connected between the first copper structure and the second yoke layer so that the tunneling current (IT) is conducted between the top and bottom surfaces of the tunnel valve sensor.
In both embodiments the tunnel valve sensor is wide so that its cross-section is large for conducting a larger tunneling current (IT). This is made possible by the yoke layer that defines the track width increasing in width as it extends into the head toward the tunnel valve sensor.
An object of the present invention is to provide a low temperature yoke type tunnel valve sensor.
Another object is to provide a high areal density tunnel valve sensor wherein top and bottom copper structures dissipate heat from the tunnel valve sensor to heat sinks and are recessed from the ABS so as to be protected from corrosion.
A further object is to provide various methods for making the aforementioned tunnel valve sensors.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.